In recent years, analysis of gene expression patterns has provided a way to improve the diagnosis and risk stratification of many diseases. For example, unsupervised analysis of global gene expression patterns has identified molecularly distinct subtypes of cancer, distinguished by extensive differences in gene expression, in diseases that were considered homogeneous based on classical diagnostic methods. Such molecular subtypes are often associated with different clinical outcomes. Global gene expression pattern can also be examined for features that correlate with clinical behavior to create prognostic signatures.
Cancer, like many diseases, is frequently not the result of a single, well-defined cause, but rather can be viewed as several diseases, each caused by different aberrations in informational pathways, which ultimately result in apparently similar pathologic phenotypes. Identification of polynucleotides that are differentially expressed in cancerous, pre-cancerous, or low metastatic potential cells relative to normal cells of the same tissue type can provide the basis for diagnostic tools, facilitates drug discovery by providing for targets for candidate agents, and further serves to identify therapeutic targets for cancer therapies that are more tailored for the type of cancer to be treated.
Identification of differentially expressed gene products also furthers the understanding of the progression and nature of complex diseases, and is key to identifying the genetic factors that are responsible for the phenotypes associated with development of, for example, the metastatic or inflammatory phenotypes. Identification of gene products that are differentially expressed at various stages, and in various types of cells, can both provide for early diagnostic tests, and further serve as therapeutic targets. Additionally, the product of a differentially expressed gene can be the basis for screening assays to identify chemotherapeutic agents that modulate its activity (e.g. its expression, biological activity, and the like).
Early disease diagnosis is of central importance to halting disease progression, and reducing morbidity. Analysis of a patient samples to identify gene expression patterns provides the basis for more specific, rational disease therapy that may result in diminished adverse side effects relative to conventional therapies. Furthermore, confirmation that a lesion poses less risk to the patient (e.g., that a tumor is benign) can avoid unnecessary therapies. In short, identification of gene expression patterns in disease-associated cells can provide the basis of therapeutics, diagnostics, prognostics, therametrics, and the like.
As another example, infectious diseases cause damage to tissues and organs that lead to the morbidity and mortality of a particular organism. In the case of influenza A infections, the most frequent cause of hospitalization and death is infection of the lung tissue. However, the precise cells that are infected by influenza, and the cells that repair the damaged lungs are not understood at the single cell level. Such knowledge could help to identify therapeutic targets for intervention, such as novel drugs to prevent viral infection and new treatments to ameliorate morbidity.
Many tumors contain mixed populations of cancer cells that might differ with respect to their signaling pathways that they use for their growth and survival. Since these cancer cells differ with respect to their response to a particular therapy, resistance of a particular population of cancer stem cells contributes to relapse after cytoxic radiotherapy and chemotherapy. As such, treatment failures in the clinic may be due partly to the resistance of a particular population of cancer cells to therapy
The often-observed initial shrinkage of a tumor soon after treatment may reflect nothing more than relative sensitivity of one sub population of cancer cells, which could comprise the bulk of a tumor, and may not be important to long term survival. Thus, the most important clinical variable for assessing treatment response and prognosis may not be the absolute tumor size but rather the absolute number of a particular population of cancer cells remaining after treatment. If one could identify differences in the signaling pathways used by these different populations of cancer cells within a tumor, then one could design therapies that target each population of cells. By targeting all populations, one could eliminate a tumor by treating with drugs that affect each different population.
As another example, inflammatory bowel disease results in disruption of the normal structure of the intestine resulting in problems such as diarrhea, bleeding and malabsorption. These problems are caused by destruction of the normal mucosal lining of the gut. The mucosal lining of the colon consists of crypts, where goblet cells, stem cells and progenitor cells are at the base of the crypt, while the mature cells including enterocytes and goblet cells reside at the top of the crypt. With inflammatory bowel disease, it is not clear which cell populations are damaged and the signaling pathways that are required to repair the damaged mucosa.
Methods of precisely determining the number and phenotype of cells in disease lesions using small numbers of cells is of great interest for prognosis, diagnosis identification of signaling pathways that can be targeted by specific therapeutics, of multiple diseases, including inflammatory bowel disease, infections, cancers, autoimmune diseases such as rheumatoid arthritis, and infections. The present invention addresses this issue.